Adapters to mount older fd mount canon lenses onto the newer eos cameras have been around for a while. There are some problems to solve. Because of the focal length, the fd lens could no longer focus to inifity and lose brightness(an f-stop). Rodolfo Novak modded his canon 55mm f1.2 fd lens for the eos mount by removing some vital parts(the attachment ring and the aperture ring). ?Now that the lens was closer, both infinite focus and the f-stop are back. He’s a bit short on the details, but it becomes clear if you look at an unmodified lens. Of course, to get the focus indicator working on a digital eos like my 350d, you need to add an af lens emulator circuit. If you don’t care about infinite focus, you could go a less invasive adapter.
The link to the af lens emulator circuit is no longer working. I am trying to do the same thing and upgrade to a digital Canon, and I’m having said problem with lenses.
He doesn’t give much detail but I think he took off all the rings up to the focus. So if your using one of the newer lenses you should have three raised screw holes and a plastic indented strip tacked on by a screw on each side. If your using an older lenses with the metal ring you should have something similar. I haven’t tried adding the EOS connector yet.
Hope that helps someone
-Mat
Here is a Canon FD 50mm prime I modded to work with infinity focus to use on my XTi. It did require me tearing apart the back of the lens and mounting an EF (EOS) adapter. It works beautifully.